The CASCADE Method. IA Cascade Method

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Edwin Kelly Gibbs
5 years ago
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1 The CASCADE Method similar to that for electromechanical devices. involves dividing the sequence into groups with each group s manifold (power or main pressure line) being supplied with pneumatic power (pressure) one at a time and in sequence. Motion within each group is powered by its own group manifold. 1

2 The CASCADE Method Step 1 Divide the sequence into Groups so that no letter is repeated within any Group. Example: START, A+, B+, B-, A-, C+, C- 2

3 Step 2: 2: For each cylinder, assign a 4/2(or 5/2) control valve with double pilot lines (i.e., without spring return) and two spring-return 3/2 limit valves to to indicate end of of strokes. START, A+, B+, B-, A-, C+, C- A B C Example 3

4 Step 3: 3: Assign one one or or more more Group Group Valves Valves or orcascade Valves Valvesto to control air air pressure to to the the Group Group manifold lines lines so so that that only only one one Group Group manifold line line is is pressurised at at any any one one time time and and in in sequence. Examples of of Cascade Valves for for 2, 2, 3 and and 4 groups.,,,, and and V V are are outputs to to Manifolds. 1,2,3 1,2,3 and and 4 are are input input control lines lines to to switch to to their their respective groups V

5 Step 3: 3: Assign one or or more Group Valves or orcascade Valves to to control air air pressure to to the the Group manifold lines so so that only one Group manifold line is is pressurised at at any one time and in in sequence. START, A+ B+ B- A- C+ C- A B C Example 1 2 5

6 Step 4 There are two approaches. Approach 1: Design according to to the sequence and using your understanding of of how the Cascade Method is is intended to to work. The principal basis is is the switching of of the Group manifolds. Approach 2: Design according to to a set of of rules worked out according to to the principles of of the Cascade Method. 6

7 Approach 1 Begin with START. nput to START comes from c- limit valve and output goes to initiate A+ motion. After A+ motion, take input to a+ from its own Group manifold and output to initiate B+ motion. START A+ B+ B- A- C+ C- A B a- a+ b- b+ c- c+ C Example START 1 2 7

8 Approach 1 At the end of the B+ motion, limit valve b+ is actuated. Connect its input to its own Group manifold and take the output signal to switch to Group. START A+ B+ B- A- C+ C- A B a- a+ b- b+ c- c+ C Example START 1 2 8

9 Approach 1 We re in Group now. First action is B-. Connect Group manifold to initiate B- motion. At the end of B- stroke, connect input of b- to its own Group and output to initiate A- motion. START A+ B+ B- A- C+ C- A B a- a+ b- b+ c- c+ C Example START 1 2 9

10 Approach 1 At end of A- stroke, a- limit valve is actuated. t then take Group power, connected to its input, and its output initiates C+ motion. At end of C+ stroke, need to use c+ to switch to Group. START A+ B+ B- A- C+ C- A B a- a+ b- b+ c- c+ C Example START

11 Approach 1 We re now into Group. First action is C-. Thus, connect Group manifold to initiate C- motion. At end of C- stroke, c- takes its input from Group and output its signal to the next action, which is START. START A+ B+ B- A- C+ C- A B a- a+ b- b+ c- c+ C Example START

12 Approach 2 Step 4 Connect the input of of the limit valve at at each stroke extremity to to its its own Group manifold START, A+, B+, B-, A-, C+, C- A B C Example

13 Step 5 For the first letter in in each Group, connect the corresponding control valve input to to its its own Group manifold START, A+, B+, B-, A-, C+, C- A B C Example

14 Step 6 For the last letter in in each Group, connect the output of of the corresponding limit valve to to switch to to the next Group START, A+, B+, B-, A-, C+, C- A B C Example

15 Step 7 For all all other letters, connect the output of of the corresponding limit valve to to the control valve input corresponding to to the next letter in in the sequence START, A+, B+, B-, A-, C+, C- A B C Example

16 Step 8 ncorporate a 3/2 spring-returned manually-operated START valve. The circuit should now be be complete START, A+, B+, B-, A-, C+, C- A B C Example START

17 Taking care of of Repeated Motions START, A+, A-, A+, A- Cylinders requiring repeated motions will need "OR" logic at the control valve. 17

18 Taking care of of Repeated Motions START, A+, A-, A+, A- For each motion, there needs to be an associated limit valve to detect end of motion. 18

19 Another example: START, A+, A-, A+, A- V V Because of repeated motion, more than one limit valves are required for each stroke extremities, one for each motion. The bottom figure is an alternative. Shuttle valves are used for the OR logic function. a+ a 1 + a

20 Another example: START, A+, A-, A+, A- V V Assign the Cascade Valves for 4 groups making sure that the connections are drawn such that Group 4 Manifold is pressurized since START is in Group 4. Draw in the four Group Manifold lines. 20

21 Another example: START, A+, A-, A+, A- V V For the first letters in each group, connect the relevant input of the cylinder control valve to its own group manifold. For this example, all the four letters are first letters. 21

22 Another example: START, A+, A-, A+, A- V V According to Step 4, connect all the inputs of all limit valves to their own group manifold lines. Connect the input of the START pushbutton to the output of the previous action, in this case, the output of limit valve corresponding to the 2 nd A- motion. 22

23 Another example: START, A+, A-, A+, A- V V The two A+s, the first A-, and START are all last actions in their respective groups. Connect the outputs of the corresponding limit valves, and of START, to switch to the next group. n the case of START, this is to switch to Group. The circuit now should be complete. 23

24 End of Cascade Method 24

Test. What type of cylinder would you use? A. Single-acting cylinder B. Double-acting cylinder Answer:

Test. What type of cylinder would you use? A. Single-acting cylinder B. Double-acting cylinder Answer: Test This test allows you to establish whether your basic knowledge of pneumatic controls is sufficient for you to attend the advanced course P or whether you should attend the basic level course P. The